Try not to worry too much about the scales that remain....you have to have a lot of scales on your tree before they will affect it's health....Be vigilant and rub off any scales you see....the ones that are "chalky" underneath is not powder, but eggs (you can see them only under a magnifyer)....if the brown scales are squishy when crushed, then these are adult females...If the tree is small and you are able to rub them off, then do so and eventually you will rid yourself of these pests....if the tree is large, then spray with the alcohol soap mixture again......Note that some scale may still be on the branches but are dead and the scale cover may just be present still clinging to the stem......as I mentioned above....don't get too alarmed.....

Thank you for your advice. I don't want to lose the sand cherry, but the thought of the scale spreading to my Japanese maple is worrisome. When I rub off the stragglers that the hose did not the scale is squishy. I will do the soap mixture again and keep at it. When I first noticed the scale it was because the tree was looking droopy so I inspected. It has also only bloomed about half what it normally does. Hopefully it perks back up.